From 6a918f0827a6e8806f77e39e0348b1a2abed71f2 Mon Sep 17 00:00:00 2001
From: "Claudius \"keldu\" Holeksa" <mail@keldu.de>
Date: Fri, 19 Dec 2025 14:11:57 +0100
Subject: Rewriting large portion for simpler approach

---
 lib/core/c++/flatten.hpp           |  44 +++++++++++++
 lib/core/c++/particle/particle.hpp |  19 +++++-
 lib/core/c++/write_vtk.hpp         | 129 +++++++++++++++++++++++++++++++++++--
 3 files changed, 187 insertions(+), 5 deletions(-)
 create mode 100644 lib/core/c++/flatten.hpp

(limited to 'lib/core/c++')

diff --git a/lib/core/c++/flatten.hpp b/lib/core/c++/flatten.hpp
new file mode 100644
index 0000000..164bb77
--- /dev/null
+++ b/lib/core/c++/flatten.hpp
@@ -0,0 +1,44 @@
+#pragma once
+
+#include <forstio/error.hpp>
+#include <forstio/codec/data.hpp>
+
+namespace kel {
+namespace lbm {
+namespace sch {
+using namespace saw::schema;
+}
+
+template<typename T, uint64_t D>
+struct flatten_index {
+public:
+	template<uint64_t i>
+	static constexpr saw::data<sch::UInt64> stride(const saw::data<sch::FixedArray<sch::UInt64,D>>& meta) {
+		if constexpr (i > 0u){
+			return stride<i-1u>(meta) * meta.at({i-1u});
+		}
+
+		return 1u;
+	}
+
+private:
+	/// 2,3,4 => 2,6,24
+	/// i + j * 2 + k * 3*2
+	/// 1 + 2 * 2 + 3 * 3*2 = 1+4+18 = 23
+	template<uint64_t i>
+	static void apply_i(saw::data<sch::UInt64>& flat_ind, const saw::data<sch::FixedArray<T,D>>& index, const saw::data<sch::FixedArray<T,D>>& meta){
+		if constexpr ( D > i ) {
+			flat_ind = flat_ind + index.at({i}) * stride<i>(meta);
+			apply_i<i+1u>(flat_ind,index,meta);
+		}
+	}
+public:
+	static saw::data<T> apply(const saw::data<sch::FixedArray<T,D>>& index, const saw::data<sch::FixedArray<T,D>>& meta){
+		saw::data<T> flat_ind{0u};
+
+		apply_i<0u>(flat_ind, index, meta);
+		return flat_ind;
+	}
+};
+}
+}
diff --git a/lib/core/c++/particle/particle.hpp b/lib/core/c++/particle/particle.hpp
index 446e8a3..b647ebe 100644
--- a/lib/core/c++/particle/particle.hpp
+++ b/lib/core/c++/particle/particle.hpp
@@ -34,10 +34,11 @@ using ParticleCollisionSpheroid = Struct<
 	Member<T, "radius">
 >;
 
-template<typename T, uint64_t D>
+template<typename T, uint64_t D, typename CollisionType = ParticleCollisionSpheroid<T>>
 using Particle = Struct<
 	Member<ParticleRigidBody<T,D>, "rigid_body">,
 	Member<ParticleMask<T,D>, "mask">,
+	Member<CollisionType, "collision">,
 	Member<T, "mass">,
 	Member<T, "size">
 >;
@@ -65,6 +66,22 @@ constexpr auto verlet_step_lambda = [](saw::data<sch::Particle<T,D>>& particle,
 		pos = pos_new;
 };
 
+/**
+*
+*
+*/
+template<typename T, uint64_t>
+constexpr auto broadphase_collision_check = [](saw::data<sch::Particle<T,D>>& left, saw::data<sch::Particle<T,D>>& right){
+	auto rad_l = left.template get<"collision">().template get<"radius">();
+	auto rad_r = right.template get<"collision">().template get<"radius">();
+
+	auto& rb_l = left.template get<"rigid_body">();
+	auto& rb_r = right.template get<"rigid_body">();
+
+	auto& pos_l = rb_l.template get<"position">();
+	auto& pos_r = rb_r.template get<"position">();
+}
+
 template<typename T, uint64_t D, typename ParticleCollision = sch::ParticleMask<T,D> >
 class particle_system {
 private:
diff --git a/lib/core/c++/write_vtk.hpp b/lib/core/c++/write_vtk.hpp
index 0647db5..7d42bc9 100644
--- a/lib/core/c++/write_vtk.hpp
+++ b/lib/core/c++/write_vtk.hpp
@@ -6,6 +6,7 @@
 #include <forstio/codec/data_math.hpp>
 
 #include "descriptor.hpp"
+#include "flatten.hpp"
 
 #include <fstream>
 #include <filesystem>
@@ -186,19 +187,139 @@ struct lbm_vtk_writer<sch::Array<sch::Struct<sch::Member<StructT,StructN>...> ,
 		return saw::make_void();
 	}
 };
+
+template<typename StructT, uint64_t Dim>
+struct lbm_vtk_writer_raw {
+	template<uint64_t i, uint64_t Dep>
+	static saw::error_or<void> write_i_iterate_d(std::ostream& vtk_file, const saw::data<StructT>* field, const saw::data<sch::FixedArray<sch::UInt64,Dim>>& meta, saw::data<sch::FixedArray<sch::UInt64,Dim>>& index){
+		constexpr auto Lit = saw::schema_type_at_index<i, StructT>::Type::KeyLiteral;
+		using Type = typename saw::schema_type_at_index<i, StructT>::Type::ValueType;
+
+		if constexpr (Dep == 0u){
+			auto flat_index = flatten_index<sch::UInt64,Dim>::apply(index, meta);
+			return lbm_vtk_writer<Type>::apply(vtk_file, field[flat_index.get()].template get<Lit>());
+		} else {
+			// Dep < Dim // I hope
+			static_assert(Dep > 0u, "Don't fall into this case");
+			for(index.at({Dep-1u}) = 0; index.at({Dep-1u}) < meta.at({Dep-1u}); ++index.at({Dep-1u})){
+				auto eov = write_i_iterate_d<i,Dep-1u>(vtk_file, field, meta, index);
+				if(eov.is_error()){
+					return eov;
+				}
+			}
+		}
+		return saw::make_void();
+	}
+
+	template<uint64_t i>
+	static saw::error_or<void> write_i(std::ostream& vtk_file, const saw::data<StructT>* field, const saw::data<sch::FixedArray<sch::UInt64,Dim>>& meta){
+		constexpr auto Lit = saw::schema_type_at_index<i, StructT>::Type::KeyLiteral;
+
+		// auto meta = field.get_dims();
+		saw::data<sch::FixedArray<sch::UInt64,Dim>> index;
+		for(saw::data<sch::UInt64> it{0}; it.get() < Dim; ++it){
+			index.at({0u}).set(0u);
+		}
+		// vtk_file write?
+		// Data header
+		{
+
+			auto eov = lbm_vtk_writer<typename saw::schema_type_at_index<i,StructT>::Type::ValueType>::apply_header(vtk_file, Lit.view());
+			if(eov.is_error()){
+				return eov;
+			}
+
+		}
+		return write_i_iterate_d<i,Dim>(vtk_file, field, meta, index);
+	}
+	template<uint64_t i>
+	static saw::error_or<void> iterate_i(std::ostream& vtk_file, const saw::data<StructT>* field,
+			const saw::data<sch::FixedArray<sch::UInt64,Dim>>& meta){
+		{
+			auto eov = write_i<i>(vtk_file, field, meta);
+			if(eov.is_error()){
+				return eov;
+			}
+		}
+		if constexpr ( (i+1u) < saw::schema_width<StructT>::value ){
+			return iterate_i<i+1u>(vtk_file, field, meta);
+		}
+		return saw::make_void();
+	}
+
+	static saw::error_or<void> apply(std::ostream& vtk_file, const saw::data<StructT>* field,
+			const saw::data<sch::FixedArray<sch::UInt64,Dim>>& meta){
+
+		vtk_file
+			<<"# vtk DataFile Version 3.0\n"
+			<<"LBM File\n"
+			<<"ASCII\n"
+			<<"DATASET STRUCTURED_POINTS\n"
+			<<"SPACING 1.0 1.0 1.0\n"
+			<<"ORIGIN 0.0 0.0 0.0\n"
+		;
+		
+		saw::data<sch::UInt64> pd_size{1u};
+		// DIMENSIONS
+
+		{
+			vtk_file << "DIMENSIONS";
+			for(saw::data<sch::UInt64> i{0u}; i.get() < Dim; ++i){
+				pd_size = pd_size * meta.at(i);
+				vtk_file << " " << meta.at(i).get(); 
+			}
+			for(saw::data<sch::UInt64> i{Dim}; i.get() < 3u; ++i){
+				vtk_file << " 1";
+			}
+
+			vtk_file << "\n";
+		}
+
+		if constexpr (saw::schema_width<StructT>::value > 0u){
+			// POINT DATA
+			{
+				vtk_file << "POINT_DATA " << pd_size.get() <<"\n";
+			}
+
+			// HEADER TO BODY
+			{
+				vtk_file << "\n";
+			}
+
+			return iterate_i<0u>(vtk_file, field,meta);
+		}
+
+		return saw::make_void();
+	}
+};
 }
 
-template<typename Struct>
-saw::error_or<void> write_vtk_file(const std::filesystem::path& file_name, const saw::data<Struct>& field){
+template<typename Sch>
+saw::error_or<void> write_vtk_file(const std::filesystem::path& file_name, const saw::data<Sch>& field){
 
 	std::ofstream vtk_file{file_name};
 
-	if(!vtk_file.is_open()){
+	if( not vtk_file.is_open() ){
 		return saw::make_error<saw::err::critical>("Could not open file.");
 	}
 
+	auto eov = impl::lbm_vtk_writer<Sch>::apply(vtk_file, field);
+	return eov;
+}
+
+template<typename StructInRaw, uint64_t D>
+saw::error_or<void> write_vtk_file(
+		const std::filesystem::path& file_name,
+		const saw::data<StructInRaw>* field, 
+		const saw::data<sch::FixedArray<sch::UInt64,D>>& meta
+	){
+	std::ofstream vtk_file{file_name};
+
+	if( not vtk_file.is_open() ){
+		return saw::make_error<saw::err::critical>("Could not open file.");
+	}
 
-	auto eov = impl::lbm_vtk_writer<Struct>::apply(vtk_file, field);
+	auto eov = impl::lbm_vtk_writer_raw<StructInRaw,D>::apply(vtk_file, field, meta);
 	return eov;
 }
 }
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